Removing oxygen from a gas



United States atent O REMOVING OXYGEN FROM A GAS Martinus L. Goedlroop, Geieen, Netherlands, assignor to Stamicarbon N .V., Heerlen, Netherlands No Drawing. Filed Dec. '12, 1952, Ser. No. 325,693 Claims priority, application Netherlands. Dec. 20, 1951 7 Claims. (Cl. 23-4-2) This invention relates to a method for removing oxygen from an oxygen-containing gas comprising contacting said gas with finely-dividedcoal at a temperature of up to 450 C. and not exceeding the softening temperature of thecoal.

Extracted nitrogen that is substantially free of oxygen is of great utility for many commercial operations. .Such oxygen-free nitrogen has been comparatively difficult to attainheretofore. It is known, for instance, that socalled Frankl apparatus can be employed in the preparation of extracted nitrogen and oxygen from air wherein the extracted nitrogen contains small amounts of oxygen, to wit, not much less than 2% by volume. By a, sharper separation the oxygen contentmay be reduced to 0.02- 0.05% by volume. This oxygen -content may be still further reduced but only by expensive methods which, for reasons of economy, are unsuitable.

A constant eifort has been maintained to produce gas, in substantially oxygen-free form so that it may be utilized commercially. Nitrogen in theoxygen-free form possesses great utility but it should be stressed that this invention contemplates the extraction of oxygen from other gases as well. It has now been found that oxygen can be removed from a gas'if the gas is brought into contact with finely-divided coal at a temperature which does not exceed 450 C. and which is always kept below the softening temperature in cases where a softening coal is employed. According to the present inventioni the coal is caused to combine with the oxygen in which process the coal is oxidized.

Bringing the oxygen-containing gas into contact with the coal results in the coal combining with the oxygen by oxidation of the coal particles, while at the same time small amounts of carbon monoxide, carbon dioxide and water are formed. By not raising the temperature to over 450 C., thedissociationo-f carbon dioxide into carbon monoxide is avoided. Removal of the carbon dioxide from the gas, which is-easily effected, leaves some carbon monoxide present in the gas instead of the originally contained oxygen.

For carrying out the process according to the present invention it should be appreciated that all kinds of coals, such an anthracite, bituminous coals-and lign-ite'may be employed. a

By the term finely divided, when used herein, is meant grain sizes not greater than 5 mm. The grain size is preferably between 0.5 and 3.0 mm. It is preferred to employ the process in cases where the oxygen concentration does not exceed by volume of the 'gas, since with higher oxygen con-ventrations the heat developed and the carbon monoxide for-med increase. The best results are achieved when-the oxygen concentration does not exceed about 3%.

By choosing a small grain size, e.g., a diameter of about 0.5-3.0 mm, a large surface area of the coal particles is obtained, by which the contact between coal and gas is promoted. Of course, a smaller diameter of grain size can be feasibly used, even as low as a diameter of 0.1 mm.

7, 2,962,343 Patented Nov. 29, 1960 It should be noted that by keeping the temperature at which the treatment is performed below the softening temperature of the coal employed, caking of the coal particles and tar formation are avoided, and good-contact of the gas with the coal particles attained.

Preferably, a coal not softening below 450 C. is utilized as heretofore noted. As a result, the treatment can be carried out at a temperature of from 360 to 380 C. and high gas velocity can be employed, for example, 50- 60 liters of gas per liter of coal per hour, the coal remaining active until it is nearly all used up and practically only the ash remains. It should be appreciated that various gas velocities can be utilized depending upon the prevailing operating conditions. If a bituminous coal softening at about 320 C. is used caking of the coal particles and tar formation can be avoided by carrying out the treatment at a temperature of from about 270 to 290 C.

Lower temperatures, below 60, may also be employed, while the treatment canalso be carried out at'room temperature without heating. However, the application of these lower temper-aturesresults in more of the oxygen combining with the coal particles so that on the surface of the coal particles a thin layer of oxidized coal is formed. As a result, the coal loses'its activity sooner than when high-er'temperatures are applied but it has been found that coal that has become inactive at low temperatures can very well be used again at higher temperatures.

In removingoxygen from gases containing amounts of from about 1 to 10% by volume of oxygen, it is desirable for maintaining the right temperature, to remove the reaction heat generated. It has-been found thattheheat development may becons-iderably lessened and the-desired reaction temperature easily maintained ifp-re-oxidized coal is used. The preoxidized coal maybe obtained by carrying out the process at a low temperature,-below 60 C., but the coal-may also'be otherwise pre-oxidized, e.g., by leading air through it.

Atmospheric pressures=rnay be employed in the subject process, but it can be appreciated that "super and-sub atmospheric pressures would also be operative. In addition,'the actual volume. of coal'to which the gas is exposed can be varied depending upou'the volume of gas intended tobe treated per stipulated period-of time. It can be appreciated that the greater the gas velocity the greater the amount of coal necessitated.

As heretofore n0ted,the process according to the invention may be applied for removing oxygen from all kinds of gases containing a small amount of oxygen, such as nitrogen, carbon monoxide, hydrogen and ;argon. In this manner the oxygen content may be reduced to less than 0.001% by volume.

The invention makes it possible to prepare'in a simple manner gases in which practically no oxygen is left, so that new possibilities arise for the application of these gases. The amount of oxygen contained in these gases had always presented difficulties in many applications.

For instance, in the preparation of oxygen in Frankl apparatus, nitrogen is also obtained, which, however, contains from 1 to"5% by volume and mostly from 2 to 3% by volume of oxygen. This in many cases precludes the useful application of this by-product.

Now the invention, by starting fromthis worthless byproduct, provides a simple manner of obtaining nitrogen suited for ammonia synthesis.

The gases purified according to the invention are also suited for analytical purposes.

The inventionenables a direct gravimetric determinationof moisture in coal-to be carried out with the help of nitrogen from which the oxygen has been extracted in the manner according to the "invention, by "heating a certain amount of coal to -110 C. while passing the nitrogen through the coal, and determining the amount of water carried off by the nitrogen. The loss in Weight of the coal must correspond with this amount of water. If in this determination of moisture, oxygencontaining nitrogen be employed, the results obtained are always deceptive as a result of the oxidation of the coal, in which process water is formed. However, this simple method of determining the moisture content can now be carried out with nitrogen treated in the manner according to the invention. It is advisable that the removal of the oxygen be carried out as a preliminary treatment of the nitrogen, before the moisture content is determined. Naturally, the nitrogen pre-treated in this manner has to be dried.

Another possibility arising from the invention is the employment of nitrogen as an inert medium in the polymerization of lactams, such as caprolactam, to form polymerization products, from which polyamide-filaments can be spun or from which articles can be made, for instance by injection moulding. If in this polymerization, oxygen-containing nitrogen is employed as the reaction medium, yellow colored polymerization products are obtained from which filaments with good and constant mechanical properties cannot be spun. Moreover, re peated breakage of the filaments occurs in spinning such products.

Now it has been found that these undesirable phenomena do not occur if the polymerization is carried out in an atmosphere of nitrogen from which the oxygen is removed in the manner according to the invention. The polymerization products thus obtained are colorless and the filaments spun out of them have good mechanical properties, while practically no breakage of the filaments occurs.

Moreover, it has been found that in arc welding, if the arc is struck in an atmosphere of argon, the drawbacks due to the presence of, generally, about 0.03% by volume of oxygen in the argon, can be avoided by employing argon from which the oxygen has been removed in the manner according to the invention.

Also water gas, which mostly contains 0.3-0.7% by volume of oxygen, can be purified in the manner according to the invention and thus be made more suitable for syntheses in which catalyst are employed.

A more complete understanding of the procedure of this invention may be had by the reference to the following illustrative examples of actual operations in accordance with the invention.

Examples 1. A vertical cylindrical vessel having a diameter of 20 cm. and a height of 3 m. was filled with finely-divided meagre coal (percentage of volatile matter: 11-14) having a grain size of from 0.5 to 1.5 mm. Through this gas-tight vessel provided with a gas-inlet and a gas-outlet, nitrogen was led upwards which had an oxygen content of 0.02% by volume. The velocity of the gas current amounted to 5-6 m. per hour. With the help of a heating jacket the temperature in the vessel was kept at 300-350 C., the nitrogen being pre-heated to about 300 C. prior to entering the vessel.

At first the nitrogen leaving the vessel was contaminated by volatile components issuing from the coal. After the nitrogen had been passing through the vessel for about half an hour a continuous current of purified gas was obtained, which was further passed through a vessel filled with silica gel. Only 0.001% by volume of oxygen was left in the purified nitrogen.

II. In a manner similar to that described in Example I, nitrogen having an oxygen content of 0.14% by volume was brought into contact with anthracite (grain-size 0.5- 1.5 mm.) at a temperature of 360-380 C. The oxygen content of the nitrogen was found to have been reduced to 0.0008% by volume.

Argon, containing 0.03% by volume of oxygen, was treated in a similar manner, as a result of which its oxygen content decreased to 0.0009% by volume.

III. In a manner similar to that described in Example I, nitrogen having an oxygen content of 0.039% by volume was brought into contact with finely-divided semi-bituminous coal (percentage of volatile matter: 17) having a grain size of from 0.5-1 mm. The temperature of the coal was kept at 270-280 C. The oxygen content was reduced to 0.0008% by volume.

IV. Nitrogen having an oxygen content of 1.6% by volume was contacted with finely-divided bituminous coal (percentage of volatile matter: 25.3) having a grain size of from 1 to 2 mm. The velocity of the gas was 5-6 m. per hour. The temperature of the coal was maintained at 4550 C. with the help of a heating jacket, while the nitrogen was not pro-heated. The oxygen content was found to have decreased to 0.0011% by volume.

The novel principles of this invention are broader than the specific embodiments recited above and rather than unduly extend this disclosure by attempting to list all of the numerous modifications which have been conceived and reduced to practice during the course of this development, these novel features are defined in the following claims.

I claim:

1. A process for removing oxygen from oxygen-containing gas, wherein the oxygen content of the gas is not more than about 3% by volume of the gas, comprising contacting said gas with finely divided coal at a temperature of from room temperature up to about 60 C. and not exceeding the softening temperature of the coal, the primary oxidation product of said process being solid oxidized coal.

2. A process according to claim 1 wherein the grain size of the coal is not less than about 0.1 mm. and not more than about 5.0 mm.

3. A process according to claim 2 wherein the grain size of the coal is not less than about 0.5 mm. and not more than about 3.0 mm.

4. A process according to claim 1 wherein the oxygen containing gas is flowed over the finely divided coal at a gas current velocity of from about 50 to 60 liters per liter of coal, per hour.

5. The process of claim 1, wherein the gas is maintained in contact with the coal for a time sufficient to reduce the oxygen content to not more than about 0.001%.

6. The process of claim 1, wherein the oxygen content of the gas is between about 0.02% and 3% and is reduced to less than about 0.001%.

7. A process for removing oxygen from oxygen-containing gas, wherein the oxygen content of the gas is not more than about 3% by volume of the gas comprising contacting said gas with finely divided coal at a temperature of from room temperature up to about 60 C. and not exceeding the softening temperature of the coal, the primary oxidation product of said process being solid, oxidized coal, said oxygen-containing gas consisting essentially of nitrogen containing less than about 3% by volume of oxygen.

References Cited in the file of this patent UNITED STATES PATENTS 914,279 Hurford Mar. 2, 1909 1,287,472 Shoeld Dec. 10, 1918 1,588,258 Netzger June 8, 1926 1,618,149 Davis Feb. 15, 1927 2,019,632 Ray Nov. 5, 1935 2,339,742 Fuchs Ian. 18, 1844 2,409,386 Pridenotf Oct. 4, 1946 FOREIGN PATENTS 13,638 Great Britain of 1904 

1. A PROCESS FOR REMOVING OXYGEN FROM OXYGEN-CONTAINING GAS, WHEREIN THE OXYGEN CONTENT OF THE GAS IS NOT MORE THAN ABOUT 3% BY VOLUME OF THE GAS, COMPRISING CONTACTING SAID GAS WITH FINELY DIVIDED COAL AT A TEMPERATURE OF FROM ROOM TEMPERATURE UP TO ABOUT 60*C. AND NOT EXCEEDING THE SOFTENING TEMPERATURE OF THE COAL, THE PRIMARY OXIDATION PRODUCT OF SAID PROCESS BEING SOLID OXIDIZED COAL. 